


Family Tree

by Nanenna



Category: Undertale (Video Game)
Genre: Alternate Universe - Underfell (Undertale), Alternate Universe - Underswap (Undertale), Cherryberry (Undertale Ship), Established Relationship, Family, Family Drama, Family Secrets, Humor, M/M, Miscommunication, Mpreg, Not that they're intentional secrets, Original Characters are fanchildren, Skeleton Pregnancy (Undertale), Spoilers, Underfell Sans (Undertale), Underfell Sans/Underswap Sans (Undertale), Underswap Sans (Undertale), no editing we die like men
Language: English
Status: Completed
Published: 2020-07-24
Updated: 2020-07-24
Packaged: 2021-03-05 04:00:29
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,479
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/25478065
Author URL: https://archiveofourown.org/users/Nanenna/pseuds/Nanenna
Summary: Papyrus has to make a family tree for a homework assignment, surely he already knows everything he needs to about that and no deep, dark family secrets will turn up to traumatize him.
Relationships: Sans/Sans (Undertale)
Comments: 16
Kudos: 66





	Family Tree

**Author's Note:**

  * Inspired by [Red's College Days](https://archiveofourown.org/works/21523588) by [HailSam](https://archiveofourown.org/users/HailSam/pseuds/HailSam). 
  * Inspired by [Underfell](https://archiveofourown.org/external_works/763563) by Vic the Underfella. 
  * Inspired by [Underswap](https://archiveofourown.org/external_works/763566) by Morty. 



> So this is a "few years later" idea I had for Hailsam's fic "Red's College Days" that takes place when Papyrus is in 8th grade. If you haven't read the fic yet I'm sure you can figure out what's going on, but it'll make more sense if you have. It's a good fic, I encourage you to go read it!

Papyrus sat down at the dinner table with his large piece of poster board, a collection of markers, and pre-cut out pictures of all his family members. His health class was doing a unit all about genealogy and families, the whole class had been given the assignment to do a family tree at least three generations back, more if possible. They’d been given two whole weeks to do it, but Papyrus already knew his family tree pretty well so he’d put it off in favor of other homework assignments due sooner. He was sure one Sunday afternoon would be plenty of time to make the best family tree! He was pretty sure he wouldn’t even need all of the marker colors, the teacher had given them a printout stating certain colors showed certain relationships like marriage or adoption. But Papyrus was nothing if not prepared! After all it contained several letters from his name.

He started by pasting his own picture right in the bottom center of the poster, then started drawing the tree up and around himself, switching out colors the few times it was needed. Mostly just the blue for his parents’ and grandparents’ marriages. Then it got a little confusing when he was ready to put Sans, his older brother, on the tree. He knew from visits to the graveyard that Sans went to go visit his birth mother’s grave, so obviously that meant their mom wasn’t his birth mom. That must mean they had the same dad, but he wasn’t sure how exactly that had happened. Had Dad been married to Sans’s mom before she died? Or was it just dating? A one night stand? He knows it wasn’t an affair, Mom was still in high school when Sans had been born and Papyrus knows from stories that Mom and Dad met in college.

Well he’d just paste her picture and write her name in and draw the line connecting her and Dad last. It would be really fast and easy to draw that line in with whichever color matches the relationship. That taken care of Papyrus went on to make his family tree the very best by adding glitter, sticker flower crowns, muscles, and sunglasses all over the place. The fact that putting himself in the middle meant squishing all of his younger siblings on one side of the poster while Sans only had to share the other half with their cousins was a little odd, but he had a lot of siblings at this point. It was fine.

“Whatcha doing?”

“Gah!” Papyrus threw the marker he’d been doodling with in the air in surprise. “Bitsy! Don’t sneak up on me like that!”

His annoying little sister giggled, then peeked over his shoulder. “Oh! It’s a family tree! Wait, who’s that? And why is Sans off by himself?”

“That’s Sans’s birth mother, he’s actually our half brother. You didn’t know?”

“No, I didn’t.”

“Well Mom would’ve been around 15 when he was born.”

Bitsy blinked, “Huh, I didn’t know.”

“That’s because you’re just a little baby.” Papyrus poked his sister’s nasal cavity.

“I am not! I’m almost twelve!”

“You’re still in stripes, you’re a baby.”

Bitsy crossed her arms and grumbled, cheeks puffed up in a pout.

Papyrus stood up, “I’m going to ask Sans something about his birth mom, I need it to put in the last line still. Do. Not. Touch.”

“I’m not!” Bitsy whined.

“Then we don’t have a problem!” Papyrus got up and started wandering through the house to find Sans. The twins were in the living room playing a video game, Bitsy peeled off to pester them instead of Papyrus for a bit. Papyrus continued through the house, up the stairs and through the bedrooms. Sans wasn’t in his own, but Papyrus did find him in the nursery with their two youngest siblings. “Sans, here you are.”

Sans looked up from where he was playing cars with Arial while Westminster just watched with a car stuck in his mouth. “Hey, ‘sup?”

“I’m doing a family tree and we were given specific instructions on which colors to use for specific relationships and I’m not sure what color to use for your birth mom and Dad.”

“I… huh?” Sans dropped the car and looked up at Papyrus. “Huh, I never thought about it before.”

“They weren’t married, right? They’d have told us if Dad was married to someone before Mom, right?”

Sans gave half a shrug, “I guess? Wouldn’t Dad have been really young when I was born?”

“Twenty one, right?”

They both stared at each other for a moment, then both gave shrugs. “No idea, it was all so long ago I don’t remember any of it actually happening.”

“Then we’ll just have to ask Mom, surely he’ll know!”

“Sure, makes sense.” Sans stood up and gave a stretch, then picked up Westminster. “C’mon, let’s go ask Mom. Arial, you coming with us?”

“Yeah!” Arial dropped the two cars she’d been holding the whole time and hopped to her feet. Then she ran over to Papyrus and tugged on his pants. “Pappus! Pappus up!”

He huffed and rolled his eye sockets, but he picked Arial up with a bounce that had her squealing.

The four of them tromped down the stairs and to the back of the house where their mom was sitting at his desk in the back room, Azzy on the floor kicking his feet as he doodled all over some printer paper. “Mom!” Papyrus practically yelled, the only way to get his attention when he was wearing the noise canceling headphones that meant he was working on… something. Papyrus still wasn’t quite sure what their mother spent so much time working on at his computer, but it looked very technical and sound related.

Red flinched and turned around, then pulled off his headphones, “What’s going on?”

Papyrus briefly explained his homework project yet again. “So what was the relationship between Dad and Sans’s mom?”

Red gave Papyrus a kind of funny look, then set aside his headphones and moved to heave himself out of his chair, “You know I’m not a hundred percent sure. It was such a short time between you getting dropped off and the house burning down so I never did get a full story out of him.”

“What?”

Red waddled towards the room’s exit, a hand at the small of his back. “My mom was surprisingly accepting of the whole thing, so I guess she knew already??? So I don’t know if… hey, where’s this family tree?”

“The… the dining room,” Papyrus said in confusion. “What are you talking about?”

“Our dad, you know, the guy in all the videos Sans used to watch as a kid like it was better than Sesame Street.”

Sans and Papyrus both looked at each other in alarm. What on earth was their mom going on about?!

“Here it is, let’s just have a little look see.” Red pulled the chair out from the table pretty far to accommodate the soon-to-be newest addition to the family, then plopped into the seat with a grunt before picking up Papyrus’s project. “I’ll need to double check that key your… uh… this is all wrong.”

Papyrus frowned, “So I’m starting to gather. How is it wrong?”

Red let the poster board fall back to the table, “You know I’m your brother too, right?”

“No???”

“You’re what?!”

“And neither of you are related to Blue by birth.”

“But… but he’s always been Dad???”

“How are you our brother?”

“Technically I’m his brother, not yours. Here, gimme a pen and paper and I’ll write it out.” Red pushed aside poster board, then looked up at his two oldest sons’ faces. “Well? Paper? Pen?”

That seemed to snap Papyrus out of his daze. He quickly put Arial down and ran from the room in search of pen and a paper. Arial happily climbed into Red’s lap, he protested with a grunt and a reminder to not kick the baby. Papyrus returned with a spiral bound notebook and a pen he dropped in front of Red. Once he found a blank page, Red started drawing out the correct family tree.

Azzy had his hands up on the table and was standing on his tippy toes to peek at what their mother was drawing. Shortly Bitsy, Boss, and Brom were all also in the room, watching intently as their mother finished writing out the family tree. Very likely they were just curious what had everyone gathered around. Eventually Red finished, even going so far as to grab Papyrus's markers and add a stripe of color over the pen lines he drew, carefully looking over the key Papyrus’s teacher had given him as he did so.

“Alright, so you two have the same mom, Calibri,” Red said as he tapped Calibri’s name. “But Papyrus, you and I have the same dad.” Red’s finger moved over to tap on Fell’s name. “Then after Blue and I got married we adopted the both of you,” Red’s finger moved to the green lines from Sans and Papyrus to link them up with the rest of their siblings, “just to make sure Calibri’s assh- uh… awful parents couldn’t try anything after they got out of prison. And then they had their uh… their “accident” two months later, still don’t regret it though.”

“So you’re my big brother?” Papyrus asked in confusion.

“I mean, technically you’re our kid what with the adoption and all that. But by birth? Yeah, brother.”

“So, you’re our uncle?” Boss asked as he stared up at Sans.

“Papyrus is, kinda. They’re also both your big brothers, what with the **adoption** I keep talking about.”

“I don’t know what to do with this information,” Papyrus murmured as he stared blankly down at the family tree his… his… Red wrote out.

“You can get a new poster board and write this out right this time,” Red said with his “I’m your mother and you will do as you’re told” voice.

“Oh, but I only have this one. Maybe I can turn this one over and use the back…?”

“Don’t worry, bro, I can drive ya to the store.” Sans moved to hand Westminster over to their mom, the toddler happily cuddled up to him. Then he gently led Papyrus from the room.

* * *

Papyrus looked nervous when he got home from school the next day. “Mom, I uh… the teacher sent something home.”

“Yeah?” Red asked as he quickly rinsed off his hands, then dried them. The rest of the dishes could wait. “Which teacher? What’d they send?”

“Mrs. Crocker, and I think she wants to talk??? To you??????”

Red frowned at that, this wasn’t like Papyrus at all. He took the piece of paper Papyrus offered and quickly read it over. Yes, Papyrus’s health teacher had asked for a parent teacher conference about the family tree he'd turned in. “Okay, so now tell me why Mrs. Crocker wants to talk to me.” He leaned back against the counter and crossed his arms.

“Well she uh… she didn’t like the family tree.”

Red cocked a brow.

“She said… she said it was wrong. She said I must have had it backwards, lots of students have found out that who they thought was an older sibling was actually their mom but she’s never heard it the other way around.”

Red growled angrily. “How dare she!”

“Is it wrong? I don’t understand, I wrote it down just like the one you made.”

“No, I watched you make it. Mrs. Crocker is the one who’s wrong.”

Papyrus gasped in shock, “But she’s a TEACHER!”

“Teachers can be wrong sometimes too, just like me and everyone else.”

“But…” Papyrus said faintly.

“Don’t you worry, honey. In fact go start on your homework, I’m going to take care of this right now.”

“Oh, okay Mom.”

Red impulsively pulled Papyrus into a hug, “You did just fine, sweetheart. You did nothing wrong and I’m going to make sure Mrs. Crocker knows that.”

An hour later, after a few phone calls, gathering up some paperwork, and printing out some more, Red marched into Mrs. Crocker’s classroom.

“Mr. Swap, so good of you to meet with me so quickly.”

Red stomped up to Mrs. Crocker’s desk, completely ignoring the hand she held out for him to shake in favor of slapping down three pieces of paper next to each other on her desk. Three birth certificates.

“Uh, what’s this? I…”

He slapped down another piece of paper on top of those, a freshly printed copy of a screenshot of a newspaper article. Then another, and another, and yet another.

“Mr. Swap, I don’t understand.”

“You called my baby bro a liar.”

“I… what?”

“Papyrus, my baby bro, apple of my eye socket, you called him a liar.”

Mrs. Crocker looked down at her desk in shock, then back at the seething skeleton in front of her. “No, not a liar, I just thought he was confused!”

“Then why did you bring me into this?”

“He spoke back in class, I wanted to talk about his attitude.”

“He spoke back because he wasn’t confused, you were! You accused him of being a liar without any proof, I’d talk back too if someone did that to me. Well here’s the proof he wasn’t lying! Is this enough?”

She looked back down at the old newspaper articles from about a decade ago with headlines about some sort of Mansfield family and their scandal, to the side of one was a picture of a younger Red with a bundled baby in one arm and a shy looking little skeleton child attached to the other hand. “You must understand, I’ve never heard of a sibling being called a parent before-”

“I can’t be the first person you’ve ever met who had to take care of a younger sibling.”

“Not one that’s called themself “mom” before!”

Red slapped down another paper, Papyrus’s adoption certificate.

Mrs. Crocker’s face turned beet red.

“Not many feel the need to adopt their sibling to protect them from abusive grandparents. You believe him now?”

Mrs. Crocker nodded.

“Good, here’s what you’re going to do: tomorrow you’re going to apologize to my son in front of the whole class for jumping to conclusions, and throw in a promise to actually listen to what your students have to say in the future for good measure. If my boy doesn’t come home tomorrow and tell me you apologized I’m going to take my complaint to the principal. We clear?”

“Y-yes sir.”

“Good.” Red swept up all the papers he’d slapped onto the teacher’s desk. “Now if we’re done here I need to get back home, this _completely avoidable_ situation means dinner’s already been delayed. Good. Day.” With that Red stormed back out of the room, leaving a shell shocked teacher behind.

**Author's Note:**

> The second tree was just as glittery and doodled on as the first. In fact! In all the places where a picture wasn't available (like the baby that hadn't been born yet) Papyrus drew what he thinks that person will or would have looked like. Strangely enough that would be Papyrus with muscles and shades. He got an A+ on it.
> 
> Blue is sadly at work and missed all the fun, but when he gets home he gets to hear ALL about it.
> 
> Also: it was never meant to be a secret. Red and Blue just kinda... forgot to ever mention it. To them it was obvious, and I think early on they would have planned to sit down and talk it out with their boys at some point but then life just kind of kept going and it slipped from their minds.


End file.
